1. Field of the Invention
The present invention relates to a thin film transistor (TFT) substrate used for a liquid crystal display apparatus, and more particularly, to a TFT substrate that may prevent faulty pixels from occurring due to permeation of cleaning liquid.
2. Discussion of the Background
Generally, a liquid crystal display (LCD) displays images using electrical and optical properties of liquid crystals that are injected into a liquid crystal panel. LCD displays have several advantages such as they may be made thin, lightweight, and they have relatively low power consumption as compared to electronic products having a cathode ray tube (CRT). Therefore, LCDs are extensively used in a variety of applications, including display devices such as laptop and desktop computers, HD imaging systems, and the like.
An LCD generally includes a liquid crystal panel assembly and a backlight assembly. The liquid crystal panel assembly may include a liquid crystal panel, a driving integrated circuit (IC), and a flexible printed circuit board. The liquid crystal panel may be formed by injecting liquid crystal material having an anisotropic dielectric constant between a TFT substrate and a color filter substrate. The driving IC applies a driving signal to a gate line and a data line formed on the liquid crystal panel. The flexible printed circuit board connects the driving IC with a printed circuit board, which transmits predetermined data and control signals to the driving IC. The liquid crystal panel assembly is combined with the backlight assembly, which includes a lamp assembly and various optical sheets, thereby forming the LCD.
Generally, the TFT substrate includes gate wiring, data wiring, and a pixel electrode. The gate wiring includes a gate line end portion, a gate line, a gate electrode, and a storage electrode line. The data wiring includes a data line end portion, a source electrode, a drain electrode, and a data line. The pixel electrode transmits a signal received through the data line to a pixel area to form an electric field in a liquid crystal layer.
The drain electrode overlaps a portion of the storage electrode line. The overlapped portion of the storage electrode line and the drain electrode forms a storage capacitor that stores a signal applied to the pixel electrode until a subsequent signal is applied.
A passivation layer may be formed on the gate wiring and the data wiring to protect them. A contact hole may be formed in the passivation layer so that a predetermined region of the drain electrode may be electrically connected with the pixel electrode. The contact hole may expose a step of the storage electrode line.
When depositing a metal material for forming the data wiring, the metal material may not be deposited on the step, thereby resulting in a crevice since the step is not favorable to the formation of a layer thereon. In particular, the step is more unfavorable to layer formation when the gate wiring and the data wiring have a multilayer structure than when they have a single-layer structure. If a crevice forms at the step, cleaning liquid may collect at the crevice when performing various cleaning processes, which may cause the data and gate wirings to erode.
Such erosion of the data wiring or the gate wiring causes a faulty pixel to occur. Accordingly, it is desired to prevent faulty pixels from occurring due to the permeation of a cleaning liquid to increase yield.